An Investigation Into the Hypoalgesic Effects of High- and Low-Frequency Transcutaneous Electrical Nerve Stimulation (TENS) on Experimentally-Induced Blunt Pressure Pain in Healthy Human Participants

Transcutaneous electrical nerve stimulation (TENS) is a noninvasive technique used to reduce pain. It is claimed that TENS frequency is a key determinant of outcome. This study compared TENS delivered at 3 pulses per second (pps) and 80 pps on blunt pressure pain in human participants when TENS intensity was standardized at a strong nonpainful level. Thirty-two pain-free participants completed an experiment in which they received TENS at 3 pps and 80 pps in a crossover fashion. An algometer was used to measure pain threshold for each frequency before and during 20 minutes of TENS. A statistically significant elevation in pain threshold relative to baseline was found for 80 pps when compared to 3 pps after 10 and 20 minutes of TENS (P = .001 and P < .001, respectively). After 20 minutes of TENS, 30 of 32 participants had exceeded a 10N elevation in threshold relative to baseline during 80 pps compared to 19 participants during 3 pps (odds ratio 10.3 (CI, 2.28, 44.78), P = .002). We suggest that the higher rates of impulse generation by TENS at 80 pps resulted in a stronger afferent input to the central nervous system, resulting in stronger segmental inhibition of nociceptive transmission of second-order neurones, in line with the gate control theory of pain. In conclusion, strong nonpainful TENS at 80 pps was superior to 3 pps at increasing pressure-pain threshold in healthy volunteers. We recommend a follow-up study using pain patients. Perspective: This study provides evidence that high frequency TENS at 80 pulses per second increases pain threshold to pressure algometry in healthy participants over and above that seen with low frequency TENS at 3 pulses per second when a strong nonpainful TENS sensation is experienced within the site of experimental pain. (C) 2010 by the American Pain Society